Watercolor is unlike any other artistic medium. It has a translucent, luminous quality. It can be applied in delicate layers to achieve subtle variations in color, and it can be used to create a wide variety of beautiful textures and patterns.
Since it is possible to characterize the most important effects of watercolor, it is clearly desirable to simulate these characteristics automatically, with a computer. It is apparent that computer generated watercolor can be used as part of an interactive watercolor paint system, or alternatively, as a method for automatic image "watercolorization."
A watercolor simulator should be largely empirically-based; it may incorporate some physically-based models, but need not be a strict physical simulation. Instead, the simulator should enable the user to re-create, synthetically, the salient features of watercolor in a way that is both predictable and controllable. Absolute physical realism is only a secondary goal.
There exists a long line of important work on simulating artists' traditional media and tools. However, the prior art does not address certain areas. Relative to the prior art on this topic, a more sophisticated paper model, a more complex shallow water simulation, and a more realistic rendering and optical compositing of pigmented layers is needed. Further, a novel approach is required that will provide many additional watercolor effects such as edge darkening, hard edges, backruns, and separation of pigments. These effects are necessary to produce a look that is much closer to real watercolors, and to capture more of the feeling of transparency and luminosity that is characteristic of the medium. An optical compositing method is particularly important for getting the appropriate look for transparency of multiple layers.
In the commercial realm, certain watercolor effects are provided by prior art products such as Fractal Design Painter and by a plug-in for Adobe Photoshop. Yet, these products do not appear to give as realistic watercolor results as would be desired. Others working on this topic have explored the effects of sumie painting, and that work has been applied to calligraphy. A related prior art model of ink diffusion through paper resembles, to some extent, the water simulation techniques useful in producing the characteristic pigment flow of watercolor.
Other research work on modeling thick, shiny paint and the effects of bristle brushes on painting and calligraphy is also relevant to this problem, by providing a plausible simulation of traditional artists' tools. It may be desirable to include a brushstroke model in the simulation process to enable the creation of the bristle patterns in a dry brush effect. The brushstroke model would thus serve as a complement to paper texture effects in the dry brush model.